1. Field of the Invention
The present invention relates to an arc evaporator, a method for driving the arc evaporator, and an ion plating apparatus.
2. Description of the Related Art
A various types of evaporation sources are used in an ion plating apparatus. One of such evaporation sources is an arc evaporation source.
In the ion plating apparatus using the arc evaporation source, when the apparatus is activated, arcing is generated between a cathode as the arc evaporation source and an anode, a cathode material is melted and evaporated in an arc spot of the cathode, the evaporated cathode material is ionized by electrons traveling from the cathode toward the anode, and the ionized cathode material is attached onto and deposited on a surface of a substrate held by a substrate holder. Thus, a thin film made of the cathode material is formed on the surface of the substrate.
Ideally, in the ion plating apparatus, the cathode material in the form of atoms flies from the cathode and is attached onto the surface of the substrate. In this ideal plating state, the thin film formed on the substrate has a smooth surface. In the case of using a high melting point material such as titanium as the cathode material, the cathode material in the form of atoms flies, allowing a thin film to have a smooth surface.
On the other hand, in the case of using a low melting point material such as aluminum as the cathode material, a melted and liquid cathode material (macro particles) flies, causing a thin film to have a roughened surface.
As a solution to this, an arcing current of the arc evaporation source might be reduced to cause temperature of the arc spot of the cathode to be lowered. However, since the reduction of the arcing current to excess brings about unstable arcing, this method is incapable of preventing the surface of the thin film from being roughened when the low melting point material is used as the cathode material.
The present invention has been developed for solving the above-described problem, and an object of the present invention is to provide an arc evaporator, a method for driving the arc evaporator, and an ion plating apparatus that are capable of preventing a surface of a thin film from being roughened when forming the thin film using a low melting point material as a cathode material.
According to the present invention, there is provided an arc evaporator comprising: an anode; an evaporation source electrode as a cathode; and a current control unit for supplying an AC square wave arcing current across the anode and the evaporation source electrode.
With this constitution, by suitably changing the square waveform of the arcing current, the average value of the arcing current can be reduced while maintaining the arcing. Therefore, the temperature of the arc spot can be lowered. As a result, the particle size of the evaporated particles can be made smaller and the surface of the thin film formed on the substrate can be thereby prevented from being roughened. In addition, since the average value of the arcing current can be reduced, the ion plating can be conducted at low temperature.
In this case, the AC square wave arcing current may have a positive value period shorter than a negative value period in a cycle. Thereby, the average value of the arcing current can be effectively reduced.
Also in this case, a frequency of the AC square wave arcing current may be 400 Hz or more. Thereby, since an absolute period during which the arcing current has a negative value is shortened, the arcing can be sustained even if the ratio of the positive value period to the negative value period of the arcing current can be reduced to reduce the average current.
Also, a frequency of the AC square wave arcing current may be between 1 kHz and 10 kHz. Thereby, since the absolute period during which the arcing current has a negative value can be further shortened, the arcing can be suitably sustained.
In the arc evaporator, the current control unit may be capable of controlling at least one of a frequency of the AC square wave arcing current, a ratio of the positive value period to the negative value period in the cycle, and a ratio an absolute value of a positive value to an absolute value of a negative value in the cycle. Thereby, the square waveform of the arcing current can be changed so as to prevent the surface of the thin film formed on the substrate from being roughened.
The arc evaporator may further comprise: a particle-size sensor for detecting a particle size of evaporated particles made of a cathode material evaporated from the evaporation source electrode, and the current control unit is adapted to control an average value of the arcing current based on the particle size detected by the particle-size sensor. Thereby, the arcing current can be controlled to allow the evaporated particles to have a desired particle size.
In this case, the particle-size sensor may comprise: a pair of electrodes placed opposite to each other, between which a DC electric field is formed; a particle collector for capturing the evaporated particles passing through a space between the pair of electrodes and thereby deflected by a predetermined amount; and a current detecting circuit for detecting a value for a current caused by the evaporated particles captured by the particle collector. Thereby, the constitution of the particle-size sensor for the evaporated particles can be simplified.
Also, the particle-size sensor may comprise: a light emitting unit for emitting light toward a portion of a surface of a substrate on which the evaporated particles are attached and formed into a thin film; a light receiving unit for detecting intensity of the light emitted from the light emitting unit and reflected on the surface of the substrate; and a control circuit for detecting a ratio of intensity of the light emitted from the light emitting unit to the intensity of the light detected by the light receiving unit. Thereby, the constitution of the particle-size sensor for the evaporated particles can be simplified.
According to the present invention, there is also provided a method for driving an arc evaporator which has an anode, an evaporation source electrode as a cathode, and a current control unit for supplying an AC square wave arcing current across the anode and the evaporation source electrode, the method comprising: controlling at least one of a frequency of the arcing current, a ratio of a positive value period to a negative value period in a cycle, and a ratio of an absolute value of a positive value to an absolute value of a negative value in the cycle. Thereby, the arcing current can be controlled to allow the evaporated particles to have a desired particle size.
In this case, the frequency of the arcing current may be controlled. Thereby, since the absolute period during which the arcing current has the negative value changes according to the frequency, the arcing current can be sustained by suitably setting the frequency.
In the method for driving the arc evaporator, the ratio of the positive value period to the negative value period in the cycle of the arcing current may be controlled. Thereby, since the average value of the arcing current changes according to the ratio of the positive value period to the negative value period, the average value of the arcing current, and hence, the particle size of the evaporated particles can be changed by changing the ratio of the positive value period to the negative value period. In addition, since the evaporation rate of the evaporated particles changes according to the ratio of the positive value period to the negative value period, it can be changed by changing the ratio of the positive value period to the negative value period.
Also, in the method for driving the arc evaporator, the ratio of the absolute value of the positive value to the absolute value of the negative value in the cycle of the arcing current may be controlled. Thereby, since the average value of the arcing current changes according to the ratio of the absolute value of the positive value to the absolute value of the negative value, the average value of the arcing current, and hence, the particle size of the evaporated particles can be changed by changing the ratio of the absolute value of the positive value to the absolute value of the negative value.
According to the present invention, there is provided an ion plating apparatus comprising: a vacuum chamber; a substrate holder provided in the vacuum chamber for holding a substrate; and an arc evaporator that uses an AC square wave arcing current to evaporate a cathode material in the vacuum chamber. With this constitution, the surface of the thin film formed on the substrate can be prevented from being roughened. Further, since the average value of the arcing current can be reduced, the ion plating can be carried out at low temperature.
According to the present invention, there is further provided an ion plating apparatus capable of performing ion plating and plasma chemical vapor deposition (CVD) in one chamber. With this constitution, since the chamber is evacuated once to conduct both of the ion plating and the plasma CVD, the production cost can be reduced.
In this case, the ion plating apparatus may comprise: a chamber having an exhaust port and a material gas supply port through which a material gas is supplied; an exhaust pump for exhausting the chamber through the exhaust port; a substrate holder provided in the chamber for holding a substrate; an arc evaporator for evaporating a cathode material in the chamber; means for opening/closing the material gas supply port; an openable cover that covers a cathode material evaporation portion of the arc evaporator; and a radio frequency power supply for generating a plasma in the chamber. With this constitution, the cover of the cathode material evaporation portion of the arc evaporator is opened and the material gas supply port is closed to conduct the ion plating, while the cover of the cathode material evaporation portion is closed and the material gas supply port is opened to conduct the plasma CVD. In this way, the ion plating and the plasma CVD can be carried out in one chamber. In general, a surface of the substrate that is to be coated has a three-dimensional shape. In this ion plating apparatus, since there is no restriction in the operation attitudes of the arc evaporation sources, a required number of arc evaporation sources can be installed at positions optimized for film formation onto the substrate. As a result, the ion plating of the present invention can be conducted suitably as compared to the ion plating using an evaporation source using resistance heating.
Further, in this case, the arc evaporator may use an AC square wave arcing current to evaporate the cathode material. With this constitution, the surface of the thin film formed on the substrate can be prevented from being roughened.
According to the present invention, there is further provided an ion plating apparatus comprising: a vacuum chamber; a substrate holder provided in the vacuum chamber for holding a substrate; an arc evaporator that uses an AC square wave arcing current to evaporate a cathode material in the vacuum chamber; and a radio frequency power supply for generating a plasma in the vacuum chamber. With this constitution, since the AC square wave arcing current is used in the evaporator even in the case where the ion plating is conducted by applying a radio frequency power in the vacuum chamber, the average current can be reduced to lower the temperature of the cathode material evaporation portion.
According to the present invention, there is still further provided an arc evaporator comprising: an anode; an evaporation source electrode as a cathode; a current control unit for supplying an arcing current across the anode and the evaporation source electrode; and a deflecting unit for deflecting evaporated particles made of a cathode material evaporated from the evaporation source electrode. With this constitution, since the substrate holder is placed on the course of the deflected evaporated particles and is not situated in front of the evaporation source electrode, the increase in the temperature of the substrate due to the radiant heat from the evaporation source electrode can be prevented.
In this case, the arc evaporator may further comprise means for rotating the deflecting unit. With this constitution, since a number of substrates can be ion-plated simultaneously and without being rotated by placing these substrates annularly forward of the evaporation source electrode.
According to the present invention, there is still further provided an arc evaporator comprising: an anode; an evaporation source electrode as a cathode; and a current control unit for supplying an arcing current across the anode and the evaporation source electrode, the arcing current having a waveform that rises substantially vertically with respect to a time axis and then falls gradually or in steps. Thereby, since the material to be evaporated is first heated rapidly by the steeply rising arcing current and then the arcing current immediately starts falling, the particle size of the evaporated particles can be prevented from becoming large-sized. As a result, the surface of the thin film formed on the substrate can be suitably prevented from being roughened.
In this case, the waveform of the arcing current may be a santooth wave. Thereby, the particle size of the evaporated particles can be suitably prevented from becoming large-sized, and thereby, the surface of the thin film made of the evaporated material can be suitably prevented from being roughened.
Also in this case, the waveform of the arcing current may be a repeated step wave. Thereby, the particle size of the evaporated particles can be suitably prevented from becoming large-sized and, thereby, the surface of the thin film made of the evaporated material can be suitably prevented from being roughened.
According to the present invention, there is still further provided an ion plating apparatus comprising: a vacuum chamber; a substrate holder provided in the vacuum chamber for holding a substrate; and an arc evaporator that uses an arcing current to evaporate a cathode material in the vacuum chamber, the arcing current having a waveform that rises substantially vertically with respect to a time axis and then falls gradually or in steps. Thereby, the surface of the thin film made of the evaporated material can be prevented from being roughened.
According to the present invention, there is still further provided an ion plating apparatus comprising: a vacuum chamber; a substrate holder provided in the vacuum chamber for holding a substrate; and an arc evaporator that uses an arcing current to evaporate a cathode material in the vacuum chamber, the arcing current having a waveform that rises substantially vertically with respect to a time axis and then falls gradually or in steps; and a radio frequency power supply for generating a plasma in the vacuum chamber. Thereby, the surface of the thin film made of the evaporated material can be prevented from being roughened.
The above and further objects and features of the invention will more fully be apparent from the following detailed description of the accompanying drawings